1. Field of the Invention
This invention relates to medical devices and techniques and more particularly relates to an electrosurgical jaw structure for thermally welding the margins of a transected tissue volume, as well as for providing highly elongate jaw members is a small cross-section that apply high compressive forces to Fred tissue.
2. Description of the Related Art
In various open and laparoscopic surgeries, it is necessary to seal or meld the margins of transected tissue volumes, for example, a transected blood vessel or a tissue volume containing blood vessels. In a typical procedure, a deformable metal clip may be used seal a blood vessel, or a stapling instrument may be used to apply a series of mechanically deformable staples to seal the transected edge a larger tissue volume. Such mechanical devices may create a seal that leaks which can result in later complications.
Various radiofrequency (Rf) surgical instruments for sealing transected structures have been developed For example, FIG. 1A shows a sectional view of paired electrode-jaws 2a and 2b of a typical prior art bi-polar Rf grasper grasping a blood vessel. In a typical bi-polar jaw arrangement, each jaw lace comprises an electrode and Rf current flows across the tissue between the first and second polarities in the opposing jaws that engage opposing exterior surfaces of the tissue. FIG. 1A shows typical lines of bi-polar current flow between the jaws. Each jaw in FIG. 1A has a central slot adapted to receive a reciprocating blade member as is known in the art for transecting the captured vessel after it is sealed
While bi-polar graspers as in FIG. 1A can adequately seal or weld tissue volumes that have a small cross-section, such bi-polar instrument are often ineffective in sealing or welding many types of anatomic structures, e.g., (i) substantially thick structures, (n) large diameter blood vessels having walls with thick fascia layers f (see FIG. 1A), (iii) bundles of disparate anatomic structures, (iv) structures having walls with irregular fibrous content.
As depicted in FIG. 1A, a relatively large diameter blood vessel falls into a category that is difficult to effectively weld utilizing prior art instruments. A large blood vessel wall has substantially thick dense and non-uniform fascia layers underlying its exterior surface. As depicted in FIG. 1A, the fascia layers f prevent a uniform flow of current from the first exterior surface s to the second exterior surface s of the vessel that are in contact with electrodes 2a and 2b. The lack of uniform bi-polar current across the fascia layers f causes non-uniform thermal effects that typically result in localized tissue desiccation and charring indicated at c. Such tissue charring can elevate impedance levels in the captured tissue so that current flow across the tissue is terminated altogether. FIG. 1B depicts an exemplary result of attempting to weld across a vessel with flick fascia layers f with a prior art bi-polar instrument. FIGS. 1A-1B show localized surface charring c and non-uniform weld regions w in the medial layers m of vessel. Further, FIG. 1B depicts a common undesirable characteristic of prior art welding wherein thermal effects propagate laterally from the targeted tissue causing unwanted collateral (thermal) damage indicated at d.
A number of bi-polar jawed instruments adapted for welding and transecting substantially small structures have been disclosed, for example: U.S. Pat. No. 5,735,848 to Yates et al.; U.S. Pat. No. 5,876,410 to Schulze et al.; and U.S. Pat. No. 5,833,690 to Yates et al. One other similar bi-polar instrument was disclosed by Yates et al. in U.S. Pat. No. 5,403,312. In that patent, paired bi-polar electrodes are provided in left and right portions of a jaw member to induce current flow therebetween. It is not known whether a jaw having the left-to-right or side-to-side bi-polar current flow of U.S. Pat. No. 5,403,312 was ever tested but it seems likely that such an instrument would confine current flow to the tissue""s exterior surface and facial layers f (see FIG. 1B), thus aggravating the desiccation and charring of such surface layers.
What is needed is an instrument working end that can utilize Rf energy in new delivery modalities: (i) to weld a transected margin of a substantially thick anatomic structure; (ii) to weld or seal a margin of a blood vessel having thick or non-uniform fascia layers; (iii) to weld or seal tissue volumes are not uniform in hydration, density and collagenous content; (iv) to weld a transected margin of a bundle of disparate anatomic structures, and (v) to weld a targeted tissue region while substantially preventing collateral thermal damage in regions lateral to the targeted tissue.
The object of the present invention is to provide a novel techniquexe2x80x94and an instrument working end capable of practicing the techniquexe2x80x94for causing controlled Rf energy delivery and controlled thermal effects in a transected margin of tissues with thick facial layers, or other tissue with non-uniform fibrous content. For example, larger diameter blood vessels are a targeted application since such vessels have thick facials layers that can prevent uniform current flow and uniform resistive heating of the tissue.
As background, the biological mechanisms underlying tissue fusion by means of thermal effects are not fully understood. In general, the delivery of Rf energy to a captured tissue volume elevates the tissue temperature and thereby at least partially denatures proteins in the tissue. The objective is to denature such proteins, including collagen, into a proteinaceous amalgam that intermixes and fuses together as the proteins renature. As the treated region heals over time, the so-called weld is reabsorbed by the body""s wound healing process.
In order to create an effective weld in a tissue volume with substantial fascial layers, it has been found that several factors are critical. The objective is to create a substantially even temperature distribution across the targeted tissue volume to thereby create a uniform weld or seal. Fibrous tissue layers (i.e., fascia) conduct Rf current differently than adjacent less-fibrous layers, and it is believed that differences in extracellular fluid contents in such adjacent tissues contribute greatly to the differences in electrical resistance It has been found that by applying very high compressive forces to a tissue volume comprising fascia layers and adjacent non-fibrous layers, the extracellular fluids either migrate from the non-fascial layers to the fascial layers or migrate from the captured tissue to collateral regions. In either event, high compressive forces tend to make the resistance more uniform regionally within the captured tissue volume. Further, it is believed that high compressive forces (i) cause protein denaturation at a lower temperature which is desirable, and (ii) cause enhanced intermixing of denatured proteins thereby creating a more effective weld upon tissue protein renaturation.
Also, it has been found that that a critical factor in creating an effective weld across adjacent fibrous (fascia) layers and non-fibrous (medial) layers is the deliver of bipolar Rf energy from electrode surfaces engaging the medial layers and the surface or fascia layers In other words, effective current flow through the fascia layers is best accomplished by engaging electrodes on opposing sides of the fascial layers. Prior art jaw structures that only deliver bi-polar Rf energy from outside the surface or fascial layers cannot cause effective regional heating inward of such fascial layers. For this reason, the novel technique causes Rf current flow to-and-from the medial (or just-transected) non-fascia layers of tissue at the interior of the structure, rather than to-and-from exterior surfaces only as in the prior art. This method is termed herein a medial-to-surface bi-polar delivery approach or a subfascia-to-fascia bi-polar approach.
Another aspect of the invention provides means for increasing the area of the engagement interface between an electrode and the just exposed medial tissue layers. This is accomplished by providing a wedge-like slidable member having an electrode surface for compressing the just-transected tissue volume against inner faces of the paired jaw members.
More in particular, the working end of he instrument carries a jaw assembly with paired first and second jaws for engaging and compressing tissue along a line targeted for transection. The transected tissue margins thereby expose medial tissue layers m that can be engaged by an electrode. The jaw structure is moveable between a fist (open) position and a second (closed) position by a slidable blade member that serves two functions: (i) to transect the captured tissue, and (ii) to contemporaneously lock together the elongate jaws by means of xe2x80x9cIxe2x80x9d-beam flanges that span both sides of the paired jaws.
The combination of the first and second jaws together with a cooperating slidable transecting (or blade) member further provides a novel electrode arrangement that can accomplish the electrosurgical welding technique of the invention. The opposing jacks carry electrodes sources coupled to an Rf generator that have a common polarity. In other words, Rf current does not flow directly from the first jaw to the second jaw (in contrast to prior art, see FIG. 1A). Rather, the extension portion of the slidable transecting member carries, or comprises, an electrode of an opposing polarity. Thus, when the transecting member is moved to the ended potion after transecting the engaged tissue volume, the elongate electrode carried by the transecting member will thus engage the medial or interior layers of the transected margin. By this means, for the first time, bipolar current flows can be directed from the transecting member that engages medial or subfascial tissue layers to both jaw faces that engage opposing surface or fascial tissue layers of the targeted tissue volume. It has been found that by engaging the medial portion of a just-transected structure with a first bi-polar electrode, and an exterior of the structure engaged with a second cooperating electrode, substantially uniform current flow through thick or non-uniform fascia layers can be accomplished This novel medial-to-surface bi-polar approach of the invention also seems to greatly reduce tissue charring, and substantially prevents collateral thermal damage in the tissue by reducing stray Rf current flow through tissue lateral to the engaged tissue.
Of particular interest, the invention provides other (optional) features that enhance the effectiveness of an medial-to-surface bi-polar approach. More in particular, it has been found that increasing the electrode engagement area with the medial tissue layers can enhance thermal effects for tissue welding For this reason, the elongate transecting member electrode may be configured as a wedge-type with an increasing cross-section that is adapted to plow into the medial tissue layers thereby increasing the electrode-tissue engagement area.
Also of particular interest, the invention provides means for highly compressing the engaged tissue between the electrode surface engagements, which has been found to assist in creating an effective weld. Such tissue compression is accomplished by using a flanged transecting member that compresses and maintains the jaws in a closed position over the entire length of the jaws
In another embodiment of the invention, the jaw assembly further includes components of a sensor system which together with a power controller can control Rf energy delivery during a tissue welding procedure. For example, feedback circuitry for measuring temperatures at one or more temperature sensors in the jaws may be provided Another type of feedback circuitry may be provided for measuring the impedance of tissue engaged between the transecting member and a jaw. The power controller may continuously modulate and control Rf delivery in order to achieve (or maintain) a particular parameter such as a particular temperature in tissue, an average of temperatures measured among multiple sensors, a temperature profile (change in energy delivery over time), or a particular impedance level or range.
Additional objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.